The invention has for its subject-matter an intrabuccal detector for X-ray apparatus of the kind employed in stomatology.
As is known, the most advanced X-raying techniques have been using since long stomatologic X-ray apparatus which comprise an intrabuccal detector or sensor responsive to X-radiation from an external source, a signal processing unit connected by a cable to the intrabuccal detector or sensor, and a device connected to the processing unit and capable of displaying the X-ray picture received by the detector.
Studies constantly directed to improving this radiological technique have shown that the cited intrabuccal detector or sensor is de facto the most important element in the apparatus in question in that it affects most their functionality.
In fact, whereas the other parts of such apparatus can be designed unrestrictedly because external to the patient and possibly located away from the X-ray source, the detector must be provided quite small in order to fit in the patient's mouth in a plurality of positions.
In addition, the intrabuccal detector is the single source of the imaging signals sent to the processing unit, and accordingly, if its resolutive power is poor, the processing unit will be unable to produce adequately sharp pictures, regardless of how powerful the unit may be.
It should be also considered that the intrabuccal detector is not only to output signals to the processing unit but also to itself process said signals in part, in order for the latter to be transmitted over a preferably long and thin cable that causes no inconvenience for the patient.
Also, tied to the responsiveness of the intrabuccal detector or sensor is the strength of the radiation to be emitted by the X-ray source, and it is essential that such radiation strength be as low as possible not to be harmful for the patient in view of that several radiographs of the mouth may be necessary in some cases.
The most widely used of known intrabuccal detectors employs two elements, namely: a scintillation screen adapted to convert at least in part X-radiation into visible light, and a CCD (Charge Coupled Device) sensor responsive to the light emission from the scintillation screen and capable of converting the same to electric signals.
CCD sensors are highly expensive and are generally small in size, whilst scintillation screens are much cheaper and must have large dimensions equal to those of the mouth region to be radiographed.
Thus, there exists the problem of how to relate the broad surface of the screen to a smaller surface area of the CCD sensors.
It has been known, in an attempt at solving this problem, to guide and convey the light beam from the scintillation screen to the CCD sensor by means of fiber optics set to converge.
According to this prior approach, the fiber optics are tapered and have a large cross-sectional area end in contact with the scintillation screen and a small cross-sectional area end in contact with the CCD sensor.
The approach just described is in many ways less than fully satisfactory.
First, the extent of the convergence and concentration of the light rays to be obtained by guiding them with tapering fiber optics is quite modest. This because it is impossible to provide fiber optics having greatly different end cross-sectional areas, both on account of that the small section ends cannot be made thin beyond certain limits in practice and above all that the large section ends must be also made very thin to avoid that the CCD sensor may be transmitted too coarse a picture.
In fact, fiber optics have unavoidable interstices between fibers, which interstices become enhanced as the fiber cross-section increases. The generally circular cross-sectional shape of fiber optics makes then unacceptable bundling together relatively large cross-section fibers.
A small amount of convergence is unsatisfactory not only because it reduces the detector bulk by a minor amount and only slightly improves the picture brightness at the CCD sensor, but above all because it attenuates in no significant way the strength of the X-radiation delivered to the patient and the scintillation screen due to the resulting low increase in brightness.
Another drawback is that the arrangement of fiber optics between the screen and the sensor restricts the extent of the image processing which can be applied downstream from the intrabuccal detector: in particular, the images can only be slightly enlarged because fiber optics, albeit thin, transmit a blurred image, i.e. a point or spot one. This drawback defeats in part the possibility of having highly sophisticated electronic units arranged downstream from the detector.
A further drawback is that if the screen is linked to the sensor through said fiber optics, a detector is provided wherein the screen-fiber-sensor assembly is difficult to set up, wherein no room is allowed for any additional elements such as internal filters and the like, and wherefrom heat cannot be readily dissipated but is transferred directly by conduction to the various elements.
Thus the technical problem remains unsolved of how to make the relatively large picture on the scintillation screen to converge efficiently into a high-performance small-size CCD sensor with respect to said screen.